Reinforced gingival retraction cord

ABSTRACT

Gingival retraction cords are constructed from two or more strands that are interlocked to form a knitted, braided, woven, or twisted retraction cord. At least one strand is made from an absorbent material and another strand is made from a degradation-resistant material, such as nylon, polyester, fiberglass, or metal. The absorbent strands are impregnated with an active agent. The degradation-resistant strands resist degradation by the active agent. Alternatively, one or more strands are used to make the knit, weave, or braid and each strand is made from two or more different fibers. For example, one or more absorbent fibers and one or more synthetic fibers can be twisted to make a blended strand. The blended strands can be used to knit, braid, or weave a retraction cord. Because the degradation-resistant strands are part of the strand pattern, the retraction cords can be made sturdier without adversely affecting the cord&#39;s inherent deformation properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.10/863,974, entitled “Reinforced Gingival Retraction Cord,” filed Jun.9, 2004, now U.S. Pat. No. 7,121,828 the disclosure of which isincorporated in its entirety.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to gingival retraction cords. Moreparticularly, the present invention relates to chemically impregnatedretraction cords that have an additional strand or fiber incorporatedtherein for reinforcing or enhancing the cord.

2. The Related Technology

When performing various dental procedures, it is often desirable toretract the gingival tissue to prepare the patient's teeth for theprocedure. Taking dental impressions, placing crowns, performing bridgework, or effecting other dental restorations are examples of proceduresthat benefit from retracted gingival tissue. A widely used method forretracting gingival tissue involves the use of retraction cords whichare typically braided or knitted for increased strength, flexibility andresilience. Examples of braided or knitted gingival retraction cords maybe found in U.S. Pat. No. 4,321,038 to Porteous, U.S. Pat. No. 4,522,933to Fischer, U.S. Pat. No. 4,617,950 to Porteous et al., and U.S. Pat.No. 4,892,482 to Lococo.

The most common purpose for using a retraction cord is to retract thegingiva away from the tooth to take an accurate and reliable impressionof the tooth. It is important to make an accurate impression of thetooth when constructing artificial crowns to ensure that the crownremains properly secured to the tooth for an extended period of time. Itis particularly important to make an accurate impression of the tooth inthe area at or below the gingival margin. Failure to take an accurateimpression can result in a poorly-formed or deficient prosthesis,particularly at the gingival margin. Premature failure of a crown isoften due to poor marginal detail in the impression used to fabricatethe crown.

The person's gingiva, or “gums”, not only prevents an accurateimpression of the proper shape of a person's tooth beneath the gingiva,it may also bleed if torn or damaged by high speed cutting drills orburrs used to remove tooth material preparatory to placing a crown. Thisbleeding may further interfere with the taking of a good impressionbecause extravasated blood tends to prevent adequate cleaning and dryingof the marginal area of the tooth prior to taking an impression andtends to displace the impression material before it can set. Thus, thedual problems of contraction of the gingival cuff and the presence ofhemorrhaging tissues make it impractical to simply take an impressionfollowing shaping of the tooth with a high speed drill or burr withoutretraction of the gingiva.

To control or inhibit the tendency of the gingiva to bleed whenphysically retracted by the retraction cord and/or if accidentally cutor nicked by the high speed drill or burr, retraction cords are oftentreated with a hemostatic agent. One type of hemostatic agent includesastringents, which lock or seal off exposed blood vessels so as toarrest bleeding. U.S. Pat. Nos. 4,321,038, 4,522,933, 4,617,950 and4,892,482, referred to above, discuss the use of astringents such as“alum”, or potassium aluminum sulfate.

Many chemicals used to impregnate a retraction cord often have anadverse affect on the strength of the fibers in the retraction cord.Many retraction cords are made of knitted or braided cotton fibers. Thehemostatic agent or astringent placed in the retraction cord can degradethe cord over time making it more likely to fail during use. If fibersin the knit or braid fail during use, the dental packing instrument usedto insert the retraction cord into the sulcus can slip through thefibers and potentially cut or injure the underlying tissue. In addition,fragments of the retraction cord can remain embedded between the toothand gums. Furthermore, the expandability and resilience of theretraction cord diminishes as the integrity of the knit or weave of thecord degrades.

Therefore, what is needed is a gingival retraction cord that canproperly retract the gingiva using a hemostatic agent while alsoresisting degradation due to the hemostatic agent.

BRIEF SUMMARY OF THE INVENTION

The present invention overcomes the above-mentioned problems in theprior art by providing a gingival retraction cord that resistsdegradation when impregnated with an active agent such as a hemostaticagent. According to one embodiment of the present invention, aretraction cord is formed by interlocking two or more strands so as toform a knitted, braided, woven, or twisted retraction cord. At least oneof the strands is made from an absorbent material such as cotton. Theabsorbent strand is impregnated with an active agent such as a hemostat.

At least one other strand in the, knitted, braided or woven pattern ismade from a degradation-resistant fiber such as a polymer, ceramic, orcarbon-based material. The degradation-resistant strand provides theretraction cord with additional structural integrity by resistingdegradation caused by one or more active agents. In one embodiment, thedegradation-resistant strand comprises a thin metallic filament such assilver having a thickness less than 0.2 mm.

In an alternative embodiment, the retraction cord of the presentinvention is formed from one or more strands made from a blend offibers. One or more absorbent fibers can be twisted together with one ormore types of degradation resistant fibers to form one or morereinforced blended strands. The blended strands are then knitted,braided, woven, or twisted to form the retraction cord of the presentinvention. In this particular embodiment, each strand of the knit,braid, or weave can advantageously include one or more types ofdegradation-resistant fibers such that the entire retraction cordresists degradation.

The retraction cord of the present invention may be impregnated with anactive agent such as potassium aluminum sulfate, aluminum ammoniumsulfate, aluminum sulfate, aluminum chlorohydrate, aluminum acetate,ferric sulfate, ferric subsulfate, ferric chloride, and mixturesthereof. The absorbent strand acts as a carrier for a solution of theactive agent. When the retraction cord is packed into the sulcus betweenthe gingiva and a tooth, the active agent is released into the tissuewhere it arrests bleeding or stiffens the gingival tissue.

The degradation-resistant strand gives the retraction cord durability inthe presence of a hemostatic agent or other corrosive material. As thehemostatic agent breaks down other strands or fibers, the degradationresistant strand resists such degradation thereby preserving thestructural integrity of the cord.

The different strands and/or fibers used to make the retraction cord ofthe present invention are blended together such that each fiber orstrand follows the knit, braid, or weave pattern. In this way, theblending does not compromise the beneficial features of the braid orweave pattern. Thus, blends of absorbent and degradation-resistantstrands or fibers can provide the retraction cord with beneficialcharacteristics without compromising the benefits derived from the braidor weave pattern.

These and other features of the present invention will become more fullyapparent from the following description and appended claims, or may belearned by the practice of the invention as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent invention, a more particular description of the invention willbe rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope. The invention willbe described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1 illustrates an open-loop configuration used in knitting;

FIG. 2 illustrates a closed-loop configuration used in knitting;

FIG. 3 schematically illustrates the manner in which a single strand ofyarn can be knitted using the open-loop configuration of FIG. 1 so as toform a knitted retraction cord from a single strand;

FIG. 4 schematically illustrates the manner in which a plurality ofstrands may be interlocked and knitted using the closed-loopconfiguration of FIG. 2 so as to form a knitted retraction cord fromseveral strands;

FIG. 5 illustrates a length of knitted retraction cord formed from fourstrands according to an exemplary embodiment of the present invention,in which one strand is made from a synthetic material;

FIG. 6 illustrates a transverse cross-section of the knitted retractioncord of FIG. 5 taken along line 6—6;

FIG. 7 illustrates an alternative embodiment of the present inventionshowing a single strand of the knit being made from a blend of fibers;

FIG. 8 schematically illustrates a cross-sectional portion of a tooth,the tooth's associated gingival cuff, and a knitted retraction cordbeing packed into the gingival sulcus between the tooth and the gingivalcuff; and

FIG. 9 illustrates an exemplary retraction cord formed using severalstrands in a braided pattern.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

I. Retraction Cords

As used herein, the terms “knitting” and “knitted” relate to a processof using one or more separate strands to form a series of interlockingloops. A “strand” may include one or more fibers which are twisted orotherwise joined together.

A. Strand Pattern

Retraction cords according to the present invention can be made usingany of various techniques, including knitting, braiding, weaving, ortwisting.

As shown in FIGS. 1 and 2, two common types of knitting techniques thatcan be used to form the retraction cords of the present inventioninclude knits made from an “open” loop and a “closed loop.” The “open”loop shown in FIG. 1 is formed using a first loop 10 a that isinterlocked with an adjacent loop 12 a such that ends 14 a and 16 a ofloop 10 a do not cross one another.

In contrast, FIG. 2 illustrates what is generally known as a “closed”loop knit. The end 16 b of first loop 10 b bends back over and crossesin a manner that closes off the loop 10 b.

FIG. 3 illustrates two rows (generally designated at 18 a and 20 a) ofinterlocked loops constructed utilizing the open-loop configurationshown in FIG. 1. As seen in FIG. 3, row 18 a includes a plurality ofloops 10 a, which are interlocked with loops 12 a of adjacent row 20 a.FIG. 3 illustrates “weft” knitting, which is made from one loop to thenext in the same course, or row, of loops, and which can be done using afirst strand 21 a for row 18 a and a second strand 21 b for row 20 a.Alternatively, weft knitting can be performed using a single strand ormore than 2 strands.

As discussed more fully below, strands 21 a and 21 b are a blend or caninclude a blend of different materials to give the retraction cordbeneficial properties such as resistance to the degrading effects of ahemostatic agent or other corrosive material.

FIG. 4, alternatively, illustrates three rows (generally designated at18 b, 20 b, and 22 b, respectively) of interlocked loops constructedutilizing the closed-loop configuration of FIG. 2. As seen in FIG. 4,row 18 b includes loops 10 b, which are interlocked with the loops 12 bof adjacent row 20 b. Loops 12 b of row 20 b are in turn interlockedwith the loops 24 b of adjacent row 22 b, and so on.

FIG. 4 illustrates “warp” knitting in which several strands 26, 28, 30,and 32, are interconnected such that the interlocking loops of eachstrand connect from one row to the next. As discussed more fully below,the knitted strands can be made of one or more different materials togive the retraction cord advantageous properties.

FIG. 5 shows a gingival retraction cord 34 knitted from four strands 36,38, 40, and 42 using the closed-loop pattern shown in FIGS. 2 and 4. Thenumber and pattern of strands 36, 38, 40, and 42 is more readilyapparent in the cross sectional view of retraction cord 34 illustratedin FIG. 6.

It will be appreciated that the knitted retraction cord of the presentinvention can be constructed using either an open-loop or a closed-looppattern or system, as shown in FIGS. 1–5. Retraction cord 34 can also bemade using other kitting patterns so long as the knit pattern providessufficient elasticity and/or resilience. Furthermore, those skilled inthe art will recognize that the knit pattern can include any number ofstrands and each strand can be made from any number of fibers.

In another embodiment of the present invention, the two or more strandsare interlocked to form a braided, woven, or twisted retraction cord.

FIG. 9 illustrates an exemplary braided cord 60. Braided cord 60 hasfour pairs of strands 62, 64, 66, and 68, which each include an “a”strand and a “b” strand. The braid is formed by taking the leftmoststrand pair and passing it under over and then under successive strandsto the right. To illustrate this pattern, the braid in FIG. 9 would becontinued by taking strand pair 62 (i.e. strands 62 a and 62 b) andpassing it under strand pair 64, over strand pair 66 and under strandpair 68. Following this series of interlocking strands, strand pair 64would be the left most strand pair. Continuing the braid even furtherwould entail passing strand pair 64 under strand pair 66, over strandpair 68 and under strand pair 62, and so forth to form the braid havinginterlocking strands.

The braided cords of the present invention can include any number ofstrands that are interlocked to form the braid. Furthermore, the strandsthat are interlocked to form the braid can be pairs of strands as inFIG. 9, or can be single strands or have more than two strands.

The present invention can be carried out using other configurations ofstrands. For example, two or more strands can be placed adjacent eachother and then twisted to interlock the strands to form a twisted cord.In another embodiment, two or more strands can be interlocked to form aweave. Those skilled in the art are familiar with the different types ofbraids and weaves that can be used to form a retraction cord.

B. Strands and/or Fiber Blends

With continued reference to FIGS. 5 and 6, strands 36, 38, 40, and 42are a blend of strand materials. In an exemplary embodiment, strands 36,38, and 40 are cotton strands and strand 42 is a synthetic polymer suchas nylon or polyester. Alternatively, strand 42 can be a ceramic,carbon-based, or thin metallic strand having a thickness less than about2 mm. The blended strands are knitted to form retraction cord 34 havinga 3:1 ratio of absorbent to degradation-resistant strands. The blend canbe adjusted as desired by using more or fewer absorbent and/ordegradation-resistant strands.

It is particularly useful for metallic strands to have a thickness lessthan 0.2 mm, although other degradation-resistant strands can also havethickness less than 0.2 mm, in order for the metallic filament to retainhigh flexibility for increased comfort and ease of placement of theretraction cord. Metallic wires having a thickness of 0.2 mm or moretend to be overly stiff. To ensure that metallic or other filaments havea high level of flexibility, such filaments will preferably have athickness less than about 0.15 mm, more preferably less than about 0.1mm; and most preferably less than about 0.075 mm.

In another embodiment, a blended cord material is created by blendingtwo or more fibers to make a strand. One or more strands having blendedfibers are then knitted to make a retraction cord. FIG. 7 illustrates anexemplary strand 44 that is made from a blend of cotton fibers 46 a–46 cand a synthetic fiber 48. Fibers 46 a–46 c and fiber 48 are twistedtogether to form strand 44 having a 3:1 ratio of absorbent todegradation-resistant fibers.

It will be appreciated that strands can be made from more or fewerabsorbent fibers and/or degradation-resistant fibers such that theretraction cords of the present invention can have almost any desiredblend ratio. Furthermore, blended strands can also be blended with otherblended or non-blended strands to create a retraction cord having adesired absorption, resistance to degradation, or resiliency.

Materials used to create the blends of the present invention includenatural and synthetic polymers, coated polymers, metal filaments, or anyother threadable material that can give the retraction cord a desiredproperty. For instance, cotton can be used for its absorbency, low cost,and biocompatibility. In one embodiment a polymer fiber or metalfilament can be selected to give the refraction cord a desiredresiliency, elasticity, or deformability. A metal filament such assilver can also be included to make the retraction cord radiopaque.Other suitable materials include eaton fibers and filaments and ceramicfibers (e.g., fiberglass).

In an exemplary embodiment, a synthetic polymer such as nylon orpolyester is included in the knit of the retraction cord to resistdegradation by an active agent. As discussed below, active agents suchas hemostatic agents can be included in the retraction cord of thepresent invention to assist in controlling bleeding of the gingivalduring a procedure. Active agents that are corrosive can break downabsorbent fibers such as cotton. In accordance with one embodiment ofthe present invention, a synthetic polymer such as nylon or polyester isincluded in the knit to resist degradation and thus failure of theretraction cord. Preventing the failure of the knit helps ensure thatthe retraction cord properly retracts gingival tissue and reduces thechances that a packing instrument will pierce the knit of the cord anddamage the underlying tissue.

As mentioned above, the non-degrading fiber or filament can be blendedinto the knit through a strand or through individual fibers. In thisregard, it can be advantageous to include the non-degrading material asa fiber in each strand of the knit. In this manner, each strand isstructurally supported and improved by the blend of fibers.

Similar to the knitted retraction cords, retraction cords made using abraid, weave, twist, or other strand pattern can have any number orcombination of strands in the strand pattern. In addition, the braid,weave, or twist may have individual strands with combinations ofdifferent fibers, similar to the combinations illustrated in FIG. 7, forexample.

Referring again to FIG. 9, in one embodiment, one or more of the pairsof strands 62, 64, 66, and 68 includes an absorbent strand and adegradation-resistant strand. For example, 62 a can comprise adegradation-resistant strand and 62 b can comprise an absorbent strandsuch as cotton.

In an alternative embodiment, one or more of the individual strands ofstrand pairs 62, 64, 66, and 68 has fibers that include an absorbentfiber and/or a degradation-resistant fiber.

In yet another embodiment, the degradation-resistant strand and theabsorbent strands are different, pairs of interlocking strands. Forexample, both strands 64 a and 64 b can be made from an absorbentmaterial such as cotton and strands 66 a and 66 b can be made from adegradation-resistant strand such as a polymer.

The retraction cords of the present invention are designed to obtain thebenefit of having various different materials in the cord, withoutdestroying the benefits of the particular strand pattern. Knitted,braided, woven, and twisted cords all, have certain flexibility,resilience, and packing properties. Unlike attempts in the prior art,the blends of the present invention do not prevent the natural movementsof the cord because the degradation-resistant strands and the absorbentstrands form part of the knit, weave, twist, or braid and are flexible.

II. Active Agents

In an exemplary embodiment, the retraction cord of the present inventionincludes an active agent such as a hemostatic agent. Hemostatic agents,including astringents and other vasoconstrictors, can be impregnated inthe retraction cord to control bleeding and stiffen gingival tissue.

Active agents that may be useful in assisting hemostasis include, butare not limited to aluminum compounds such as potassium aluminumsulfate, aluminum ammonium sulfate, aluminum sulfate, aluminumchlorohydrate, aluminum acetate, other water soluble astringent aluminumsalts, and mixtures thereof. Another class of astringents includesiron-based compositions such as ferric salts, including but not limitedto ferric sulfate, ferric subsulfate, ferric chloride, and mixturesthereof. Other astringents include permanganates, tannins and zincchloride. In one embodiment the active agent is a vasoconstrictor suchas epinephrine and/or propylhexedrine.

The active agent is typically delivered to the gingival tissue in asolution, such as an aqueous solution. As discussed above, in anexemplary embodiment, retraction cord 34 includes an absorbent material.The absorbent material absorbs the solution thereby impregnating theretraction cord 34 with the active agent. While the active agent may beimpregnated using a mechanism other than a solution, a solution isbeneficial because it can easily be expressed in the sulcus.

The knitted pattern of retraction cord 34 helps absorb and deliver theactive agent. The interlocking loops of the knit pattern substantiallyincrease interstitial a volume of cord 34, which allows the retractioncord to carry larger amounts of active agent. Because the knit patterncarries additional active agent, non-absorbent strands can be blendedinto the knit pattern without affecting the hemostatic ability of theretraction cord.

Additionally, the ability of knitted retraction cords to effectivelydeliver the active agents to the gingival tissue is greatly augmented bythe fact that the knitted retraction cords are compressed when packed inthe sulcus. Thus, knitted cords may actually express the hemostatic orother active agent(s) into the small capillaries of the gingival tissuewhen compressed, thereby forcing the active agents into the bleedingpores so as to stop hemorrhage.

III. Method of Use

In FIG. 8, a dental instrument 50 is shown pressing the gingivalretraction cord 34 within the sulcus 52 between the gingival cuff 54 andthe tooth 56. The resilience and flexibility in the transverse directionallows the knitted retraction cord 34 to conform to irregularities, suchas the margin 58 of the tooth 56.

Even if the loops of the knitted retraction cord are left rather loose,because of the intricate interlocking network, there is little or notendency for the dental packing instrument to slip through theretraction cord. Rather, the compressibility of the knitted cord 34causes the cord 34 to “dimple” around the edges of the dental packinginstrument 50.

Because of the compressibility and bendability of knitted retractioncords there is less of a tendency for the cords to damage underlyinggingival tissue as force is applied during packing. This is because theforce of the packing instrument tends to be spread out over a largerarea by the interlocking loops of the knitted cord. Also, the transverseresilience of the knitted cord enables it to conform to irregularitieswithin the sulcus. Thus, the knitted cord can accomplish both horizontaland vertical retraction using a single cord.

Another advantage of knitted retraction cords is their tendency toreturn to their original, uncompressed shape because of theirresilience. Thus, when a knitted retraction cord is packed into thesulcus, it is compressed, and the “memory” in the retraction cord causesthe cord to gently push outward against the gingival tissue 54. Thisoutward pushing increases the ability of the knitted cord 34 to retractgingival tissues over conventional retraction cords.

Another advantage arising from the compressibility of knitted retractioncords is realized when retracting gingival tissue around the frontteeth. The labial gingival tissue is particularly thin and membranous ascompared to the lingual gingival tissue. Using the knitted retractioncords of the present invention the lingual gingival tissue can beadequately retracted with the knitted retraction cord only slightlycompressed, and by virtue of its compressibility and its ability tostretch and become thinner, the same cord can be packed into the sulcuson the labial side of an interior tooth without over-retracting thegingival tissue. The cord then exerts a general, steady outward force onthe tissue, which is desirable.

Another feature of the retraction cord of the present invention is thatit can be chemically impregnated with an active agent over an extendedperiod of time without compromising the knit pattern and the benefitsthat accompany a knitted cord. The degradation-resistant fibers orstrands blended into the knit of the retraction cord permit chemicalimpregnation yet give the retraction cord strength in the event that theactive agent degrades other fibers in the cord.

While there are many benefits for using a knitted cord, in some cases,braided, woven, or twisted retraction cords can be preferred. Thispreference can be because of the cost to manufacture a particular cord,or because of the experience that a practitioner may have with aparticular type of retraction cord. In any event, braided, woven, andtwisted cords are improved by including a combination of an absorbentstrand and a degradation-resistant strand according to the presentinvention.

The braided, woven, or twisted retraction cords of the present inventionbenefit from having the degradation resistant strands or fibers used inthe braid, weave, or twisted pattern. The braided, woven, or twistedretraction cords bend and pack in a manner that is typical of theparticular strand pattern type. Thus, the retraction cord bending andpacking properties are not substantially affected by the inclusion ofthe degradation resistant strands. Furthermore, the braided, woven, ortwisted retraction cords can be impregnated with an active agent andresist degradation of the cord by the active agent.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A gingival retraction cord, comprising: at least one absorbent strandand at least one flexible degradation-resistant strand interlocked so asto form a braided, woven, or twisted retraction cord that is flexible,wherein the flexible degradation-resistant strand has a thickness lessthan 0.2 mm; and wherein the absorbent strand is entirely comprised offibers that are absorbent; and wherein the degradation resistant strandis entirely comprised of synthetic fibers that aredegradation-resistant; and an active agent impregnated within theabsorbent strand of the retraction cord, wherein thedegradation-resistant strand resists degradation by the active agent. 2.A gingival retraction cord as in claim 1, wherein the flexibledegradation-resistant strand has a thickness less than about 0.15 mm. 3.A gingival retraction cord as in claim 1, wherein the flexibledegradation-resistant strand has a thickness less than about 0.1 mm. 4.A gingival retraction cord as in claim 1, wherein the flexibledegradation-resistant strand has a thickness less than about 0.075 mm.5. A gingival retraction cord as in claim 1, wherein the active agentcomprises a hemostatic agent selected from the group consisting ofpotassium aluminum sulfate, aluminum ammonium sulfate, aluminum sulfate,aluminum chlorohydrate, aluminum acetate, ferric sulfate, ferric subsulfate, ferric chloride, and mixtures thereof.